Mpcnc or low rider

I’m looking at getting a MPCNC or a lowrider and want to know which would be better.
I’m planing to 3D cut RC airplanes out of xps or epo foam.

And to clarify I am not talking about Flite Test foamboard style planes.

dimensions could be up to 50" long, 10ish" wide. Z axis would only need to be about 5-7" on the big side.
It is possible the 50" dimension could be done in two parts and glued. One full length would be ideal.

would either the MPCNC or lowrider be better or is either good?

If you’re only going to carve foam, an MPCNC that large will work. It is a bit cheaper and simpler, assuming you can get inexpensive tubing. The LR would work well too, and if you wanted to carve wood, it would be preferred at those (50") lengths and heights (5*-7"). The LR requires fewer tubes, but they have to be either 25mm or 25.4mm OD.

About the height. 5-7" is pretty large. It will make that axis much less rigid. If you’re cutting foam, NBD. But on an MPCNC, if you are cutting 3/4" plywood for something, the Z has to stretch out that 6.25" to reach the top of the wood. On a LR, the extra is under the table, and milling anything 3/4" will be just as rigid, even if uou didn’t have the 7" capacity. The other part to consider is that you won’t be able to use standard bits, because they aren’t 5-7" long. So be sure you think that through, and find some bits that will work for you.

Thanks Jeffeb3. The 5-7 is way more than I need. thinking that through that would be a 10-14" wide fuselage if I did the plane in two halves. Probably closer to 3, maybe 4 at the largest. that would be a 6-8" wide fuselage.

Your thought on the LR and tubes below the table is good to think through. then I could still do wood if a project ever cam across.

Don’t forget, with the lowrider, you’ll need really long endmills to reach down 4 inches. The mpcnc can fudge it a little because the collet sticks down past the tubes some. Even the “cheap” 4" endmills I can find on ebay are almost as expensive as the 1" surfacing endmill I have that has replaceable cutting heads.

@ Barry, good point.
Where have you found 4" end mills on ebay? I have looked and not found them yet.

in the end, I could cut multiple levels with alignment features to build up the dimensions I need.

I kind of felt the lowrider was simpler myself, mechanically at least. Why do you say the mpcnc is simpler?

It has more documentation, examples, and doesn’t require flat parts. But even separate from all that, it is less error prone, a bit.

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There’s some here.

Thanks Barry. I’ll look into it.

two more questions.
1 - what is the stack up on the LR before i get to the 4" clearance?
2 - is the dewalt router stable enough for a long bit? or will there be some wobble making the cut larger than it actually is?

Longest endmill I’ve ever used is only an inch and a half long, and it’s a quarter inch endmill for the lowrider. I do know the dewalt is more rigid than the dc motor style spindles. I would think though, for cutting hd foam, that part isn’t really going to matter. Your biggest concern would be dust collection. Foam becomes statically charged when you cut it, so it’s going to stick to everything. It will also mostly skip a centrifugal dust collector. Also leave a cutout on your table to park the router, it parks at 0, so with the long endmill sticking out, it’s going to go past the table surface.

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Thanks Barry.
and one last question below.
1st - I’m leaning toward the MPCNC. If I need to cut wood or low profile parts I can build a platform instead of lowering the Z axis.

As mentioned I’m looking at a cut area of 30x50. According to the calculator I would need 30’ of tubing.
one axis would be 60.5".
I could do this with conduit and add a few supports. Maybe do this for starting out and get stainless later.
If I go SS right away, just for calculating things out, what diameter and wall thickness would be recommended for this cut size? Should I go 1" or is 3/4" sufficient?

any recommended places to purchase the SS?

I had my mpcnc out to 5 foot square before the lowrider was released. I had midspan supports on all four outer rails. It worked okayish. Would probably be fine for foam, slightly sketchy for wood, metal will be high pucker factor. 1" stainless might help, but I don’t know for sure. Having one side of your machine being 30 inches will help with sag. Also, don’t forget, the 3/4 conduit we use is measured with the inside diameter, so it’s not really 3/4 tube, it’s bigger, so 3/4 stainless tube won’t work. The only size that works with stainless is the 1" size. So you kind of need to decide on which tube you want now, unless you don’t mind printing all the parts over again. If I were doing this, I’d stick with the conduit, it’s cheap, and if you find it too wobbly for wood, shorten the legs and put them up on wooden risers.

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Barry, that sounds like good advice.
I keep going back and forth between the Low rider and the MPCNC.
The LR seems like it would have a more ridgid Z axis with basically 4 rails, two on each side.
The electronics are the same for both right? If I go with one and want to make the other, its just the hardware and printed parts right? flat parts for the LR.

Yep, same electronics for both.